'adjoinant' originates from the Latin word 'adjungere,' where 'ad-' meant 'to' and 'jungere' meant 'to join.'

'adjungere' transformed into the Old French word 'ajoindre,' and eventually became the modern English word 'adjoinant' through Middle English.

Initially, it meant 'to join or connect,' but over time it evolved into its current meaning of 'being adjacent or contiguous.'